A Tris‐induced change in the midpoint potential of Z, the donor to photosystem II, as determined by the kinetics of the back reaction

Abstract

A new method of measuring the rate of the back reaction from the state Z + P680 Q A − in Tris‐washed chloroplasts is described. By using ratios of back reaction rates we demonstrate a Tris‐induced change in the equilibrium between Z and P680 and attribute this change to an alteration of the midpoint potential of Z by Tris treatment. We also demonstrate that the previously observed inhibition of the back reaction by ADRY reagents can be localized at Z and understood in terms of electron donation to Z + by ADRY reagents.